Focusing coil for cathode-ray tubes



p l- 1952 B. c. VAN GILDER 2,594,099

FOCUSING COIL FOR CATHODEI-RAY TUBES Filed April 22, 1950 INVENTOR ATTORNEYS Patented Apr. 22, 1952 UNITED STATES PATENT OFFICE FOCUS ING COILFOR CATHODE-RAY TUBES Burrows CorsontVan Gilder, ,North Wales, 'Pa., assignor to LT-E Circuit Breaker'Company, Philadelphia, Pa., a corporation of Pennsylvania- Application April 22, 1950, Serial No. 157,451

4 Claims. 1

My invention relates to cathode ray tubes and more particularly to focusing coils for cathode ray tubes.

In iconoscopes, kinescopes and other applications of cathode ray tubes, deflection plates and yokes in electrostatic and magnetic tubes; respectively, are required. By means of voltage .and current variations, various image patterns can be obtained. The size of the scanned raster, linearity and the aspect ratio are all determined by the deflecting plates or yokes which are placed in the neck of the tube.

However, in order to impart the proper deflection on each electron, the electron gun must emit-a stream of electrons which enter the deflection region by passin along the axis of the tube. If the electrons should diverge'from this path before the deflection region, undesirable shadow efiects and improper deflection will result.

Thus, in the section intermediate of the electron gun and the deflection region is placed a focusing coil. As is well-known in the art, the configuration of the magnetic field is such that electrons which pass along the axis of the tube are not deflected by the focusing coil-since the electrons will pass parallel to the magnetic field.

Electrons which diverge from this path are acted on by the magnetic field which cause them to rotate about the aXis parallel to the tube axis and thus produce inward radial acceleration suflicient to reverse the initial outward radial velocity and to thus .bring the beam into alignment with the tube axis as it enters the deflection region.

Heretofore the magnetic focus units were constructedof either a permanent magnet or electromagnet with variations achieved either by variation of location or external adjustment of current through the coil.

In accordance with my invention, I apply an adjustable permanent magnet which can effect large range of variations of the focusing magnetic field which is produced jointly by the permanent magnet and an electro-magnetic coil.

Accordingly, an object of my invention is to provide a novel magnet focusing device-for a cathode ray tube.

A further object of my invention isto provide a novel magnetic focusing unit for a cathode ray tube utilizing an adjustable permanentmagnet used in conjunction with an electro -magnetic coil.

A 'stillfurther object of my invention is to provide an adjustable shunt permanent magnet for a focusing cathode ray beam.

A stillfurther object is to provide a novel series permanent magnet for focusin an electron beam.

The foregoing and many other objects of my invention will become apparentv whentakenin connection with the following description and drawingsin. which:

Figure 1 is aside view of.a cathode ray tube showing one form of my novel focusing magnet using an adjustable shunt permanent magnet.)

Figure 2 is a view taken along line 2a-2 of Figure 1,,

Figure 3 is a partial view in crossesectio'n. of a modified form of adjustable permanent magnet with a series path.

Figure 4 is a partial view in cross-section of another modified form. of my focusing unit with an adjustable shunt path.

Referring to Figure 1,.the cathode ray tube H of the. usual construction comprises a conical portion with aright end [3 coated on the interior surface with a fluorescent material. Atthe left enduof the conical section is the neck l2 with a socket and electron gun indicated generally at I 0. Theelectronbeam emitted fromthe cathode gun at IU traverses the neck l2 and conicalsection and then. impinges .on the fluorescent screen surface 13. The remaining portion of the oathode raytube is not hereshown as this is wellknownin the art.

As maybe observed in. Figures 1 and 2, the electromagnet M is 'comprisedof windings I5 which are wound inside a U-shaped annulus ll. |3 I9 placed concentrically withthe axis of the neck l2. The annulus ll, I8, I9 is made ofa magnetic materialv such as silicon. steel or any other material of high permeability.

Thus, the flux lines 2| :set up by current flow in thewindings 15 will follow the magnetic path of IT, l8, l9 and through the neck I lot the tube ll. As will. be observed, themagnetic field 2| in the neck of the tube has a radial component.

It is this component which will be efiective in deflectingor focusing the electrons which have diverged from the path along the axis of the tube.

In accordance with myinvention, I provide a magnetic circuit arrangement either in the form of aby-pass magnetic path or a series path of increasedreluctance for the control of this magnetic field.

A permanent magnet [6 of hollow cylindrical form is slidably mounted on the flanged portion 20a of magnetic material 20. The magnetic piece 20 forms an integral part of a "slidably mounted unit 23 which is concentric with the eck 12 and is positioned to the left ofthe electromagnet "I 4. The permanent magnet l6 ,is-rig- 3 idly attached by screw 24 or any other suitable means to the slidable adjustable unit 23. Sliding of the unit 23 along the neck |2 will position the permanent magnet l6 with respect to the electromagnet Hi.

Figures 1 and 2 illustrate the position of the permanent magnet IS in its extreme right position where a maximum amount of the magnetic flux 22 from the magnet it will be shunted through the annular ring ll, |8, |3. In the position indicated, the magnetic field 2| will be of great strength. As the cylindrical magnet I6 is moved to the left by means of sliding unit 23, less of the lines of force will be shunted through the core material ll, 3, l9 and thus the magnetic field 2| will be materially reduced.

Thus, adjusting the axial position of permanent magnet l6 by means of sliding unit 23 and shunt 23a the desired radial magnetic field strength in the neck [2 may be obtained to give correct forming of the electron beam.

In Figure 3 I have shown the combination of the electromagnet and permanent magnet, the latter adjustable, but instead of having the permanent magnet surrounding or encasing the electromagnet coil, the permanent magnet in this case is mounted inside the electromagnetic coil.

Thus, the coil 3| (Figure 3) as in the first example is mounted on the neck of the cathode ray tube and coaxial therewith and as in the previous case is provided with a U-shaped annular magnetic core 32, 33, 34 for providing a magnetic path for the flux.

The permanent magnet 35 provided with screw threads 36 thereon with corresponding teeth on the inner surface 31 of the housing for the electromagnetic coil is concentric with the electromagnetic winding 3|. The magnetic flux resulting from current flowing from the winding of the coil 3| normally extends over the magnetic path including a magnetic core 32, 33, 34 and into the neck |2 of the tube as shown by the lines of force 4 The threaded permanent magnet 35 is rigidly attached to the disc piece 38 which is mounted on the slidable rotatable unit 33 and shunt 39a. The lines of flux 4| emanating from both the magnet 35 and coil 3| will traverse the magnetic path of the annular ring 32, 33, 34 across the air 'gap 42 and through the magnet 3 5.

As the permanent magnet 35 is rotated by means of unit 39, it will thread to the right, thus reducing the air gap 42 and reducing the reluctance of the magnetic path which will increase the magnetic lines of force in the neck |2 of the tube. When the magnet 35 is rotated to move to the left, it will increase the air gap and reluctance of themagnetic path which will thus decrease the amount of lines of force that will be in the neck |2 of the tube.

In Figure 4 I have shown a further modified form of my invention in which the permanent magnet is adjustable to increase the-series of reluctance of the magnetic path. The electromagnetic'coil 'is' wound in an -L-shaped annular core 52, 53 and encloses the neck I2 of the oathode ray tube The magnetic 'path for the flux lines 51 will be through the core material 52-53, then the focus region 56 inthe neck I2 and then the permanent magnet 55 and through the air gap 54.

The permanent magnet 55 is attached to the slidable unit 58 and shunt 58a so that when the unit 58 is moved to the left the air gap 54 will of the magnetic path, thus increasing the strength of the lines of force 51 in the neck of the tube. By proper adjustment of slide 58 the correct field strength can be obtained to give desired focusing of the electron beam.

While I have in the above shown three embodiments of my invention, it will now be understood that in general it comprises the adjustment of the magnetic lines of force available for focusing the beam by an adjustment of the permanent magnet in relation to the magnetic path of the electromagnetic coil.

In addition to this adjustment, the usual adjustments of the coil made by varying the current through the windings of the electromagnetic coil may also be made, thus providing a wide range of adjustments as well as fine or Vernier adjustments and I do not wish to be limited except as set forth in the appended claims.

I claim:

1. A cathode ray beam focusing system for a cathode ray tube comprising an electromagnet having windings and a U-shaped annulus fixedly mounted concentrically with the axis of the neck of said cathode ray tube, said windings being supported on said annulus, said annulus being made of high permeability material, a magnetic slidably mounted unit concentric with the neck of said cathode ray tube positioned on one side of said electromagnetic, said magnetic unit being slidable on the neck of said tube with respect to said electromagnet, said unit having a flanged portion, said unit also comprising a permanent magnet of hollow cylindrical form having a greater diameter than said electromagnet mounted on said flanged portion of said mag- I netic unit and slidable therewith, means for rigmeans for varying the current flow in said wind- I ings wherein said means is a variable resistor.

2. A cathode ray beam focusing system for a cathode ray tube comprising an electromagnet having windings and a U-shaped annulus fixedly mounted concentrically with the axis of the neck of said cathode ray tube, said windings being supported on said annulus, said annulus being made of high permeability material, a magnetic slidably mounted unit concentric with the neck of said cathode ray tube positioned on one side of said electromagnet, said magnetic unit being slidable on the neck of said tube with respect to said electromagnet, said unit having a flanged portion, said unit also comprising a permanent magnet of hollow cylindrical form having a greater diameter than said electromagnet mounted on said flanged portion of said magnetic unit and slidable therewith, means for rigidly attaching said permanent magnet to said slidable adjustable unit, said means being a screw, said permanent magnet being concentric with said winding and providing a variable by-pass for the flux of said winding in accordance with its position with respect to said electromagnet,

.and means for varying the current flow in said windings.

3. A cathode ray beam focusing system for a cathode ray tube comprising an electromagnet having windings and a U-shaped annulus fixedly mounted concentrically with the axis of the neck of said cathode ray tube, said windings being supported on said annulus, said annulus being made of high permeability material, a magnetic slidably mounted unit concentric with the neck of said cathode ray tube positioned on one side of said electromagnet, said magnet unit being slidable on the neck of said tube with respect to said electromagnet, said unit having a flanged portion, said unit also comprising a permanent magnet of hollow cylindrical form mounted on said flanged portion of said magnetic unit and slidable therewith, means for rigidly attaching said permanent magnet to said slidable adjustable unit, said means being a screw, said permanent magnet being concentric with said winding and providing a variable by-pass for the flux of said winding.

4. A cathode ray beam focusing system for a cathode ray tube comprising an electromagnet having windings and a U-shaped annulus fixedly mounted concentrically with the axis of the neck of said cathode ray tube, said windings being supported on said annulus, said annulus being made of high permeability material, a magnetic slidably mounted unit concentric with the neck of said cathode ray tube positioned on one side of said electromagnet, said magnetic unit being slidable on the neck of said tube with respect to said electromagnet, said unit having a flanged portion, said unit also comprising a permanent magnet of hollow cylindrical form having a greater diameter than said electromagnet mounted on said flanged portion of said magnetic unit, means for rigidly attaching said permanent magnet to said slidable adjustable unit, said means being a screw.

BURROWS CORSON VAN GILDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,985,093 Hehlgans Dec. 18, 1934 2,200,039 Nicoll May 7, 1940 2,212,206 Holst et a1 Aug. 20, 1940 2,234,720 De Tar Mar. 11, 1941 2,272,353 Ruska Feb. 10, 1942 2,416,687 Fry Mar. 4, 1947 2,418,487 Sproul Apr. 8, 1947 2,431,077 Pooh Nov. 18, 1947 2,433,682 Bradley Dec. 30, 1947 2,440,403 Jackson Apr. 27, 1948 2,442,975 Grundmann June 8, 1948 2,483,133 Gethmann Sept. 27, 1949 2,501,516 Holden Mar. 21, 1950 2,503,173 Reisner 'Apr. 4, 1950 2,533,687 Quam Dec. 12, 1950 2,533,688 Quam Dec. 12, 1950 2,533,689 Quam Dec. 12, 1950 FOREIGN PATENTS Number Country Date 521,439 Great Britain May 22, 1940 597,255 Great Britain Jan. 21, 1948 615,553 Great Britain Jan. 7, 1949 

